1. Field of the Invention
This invention pertains to a system for packaging leadless electronic and electrical components for automatic component placement machines. The system includes a carrier tape on which the leadless components are held, the reel on which the component tape is wound, and the construction of the tape itself. Leadless components include chip capacitors, chip resistors, chip transistors and chip integrated circuits in general rectangular configuration and, where applicable, cylindrical components, specifically capacitors and resistors, jumpers, mini-mold transistors, diodes and other components not specifically mentioned, provided that these components may be taped in accordance with the specifications in EIA Standard Proposal No. 1460 or, if approved, standard RS-481 as of March 1981.
2. Description of the Prior Art
With the current trend toward miniaturization of electrical and electronic components and the additional trend toward automation of manufacturing and assembly in the electrical and electronic industries, systems which automatically place small leadless components on printed circuit boards have been developed. High speed automated component production is achieved from initial manufacture through final testing. Chip component placement machines currently handle approximately 1,000 to 8,000 chips per hour. One of the major problems in systems for factory automation is the gap between packaging and placement of chips. Packaging machinery has tended to be rapid but expensive in terms of packaging chips for placement. The insertion of the packages of chips into placement machines has been cumbersome and expensive. The present invention is one of several intended to smooth the handling of chip components from final test to placement on printed circuit boards at somewhat comparable rates of speed and at reasonable cost.
With the extensive use of chip components, several methods of chip packaging have been developed for automatic placement of chips. Cassette type packages, such as that disclosed in Netherlands patent application Ser. No. 8006058, provide a means of packaging chips at the manufacturing facility in a cassette which later can be placed in an automatic multi-chip placement machine, such as that disclosed in U.S. patent application Ser. No. 235,802, filed Feb. 11, 1981. An alternative means of delivering chips to an automatic placement machine is a tape system. Tape systems have been developed and sold by a number of component companies including Panasonic (Matsushita), TDK, the DYNA/PERT Division of Emhart Corporation and others. It appears that the taping of leadless components for automatic placement will become the dominant means of delivering chip components to automatic placement machines. Accordingly, the Electronic Industries Association devoted considerable effort between 1979 and 1981 to developing standards for taping. Tape systems are based on tape dimensions similar to those of super 8 movie film, the tape being wound on reels similar to those of super 8 movie film and fed through a drive mechanism. The tentative EIA standards proposal No. 1460, which, if approved, will be published as RS-481, prescribes dimensions and tolerances required to tape leadless components such that they may be automatically placed on printed circuit boards. The EIA standard covers many leadless components, specifically chip capacitors, chip resistors and chip transistors in general rectangular configuration, as well as for cylindrical components, specifically capacitors and resistors, jumpers, mini-mold transistors, diodes and other components not specifically mentioned, provided that these components may be taped in accordance with the standards. The standard also prescribes container and reel marking requirements.
With respect to the tape, the EIA standard prescribes carrier tape dimensions based on a super 8 tape in which sprocket holes are punched along one edge of the tape and cavities are punched in the balance of the tape for components. Two standards are available for tapes, one covers a carrier tape which is frequently made of a cardboard having sprocket holes and component cavities, which are spaced recesses or apertures, punched in an eight millimeter wide cardboard carrier. Components are held in the cavities in this carrier tape by top and bottom cover tapes only 5.2 millimeters wide so that the cover tapes will not interfere with the sprocket holes. The standard also defines a plastic embossed tape in which cavities are formed by embossing in a plastic tape 8 mm wide and a 5.2 mm top cover tape is used to hold the components in place in the embossed cavities. The standard further defines reel dimensions for the reels on which tapes may be wound as well as the dimensions for drive spokes or key slots, if such drive spokes or key slots are necessary. The standard further prescribes specifications for placement of polar units within the taping system.
The proposed standard also includes related considerations. It prescribes that the components must be prevented from falling out of the component window or cavity of the tape, which is normally overcome by fixing cover tapes on one or both sides of the carrier tape. Fixing tapes or cover tapes must not protrude beyond the edges of the carrier tape nor can they cover the sprocket holes. Tapes in adjacent layers must not stick together in packing or winding. The adhesive of the fixing tape should not adversely effect the mechanical and electrical characteristics and marking of the components. The tapes must be suitable to withstand the storge of the taped components without danger of migration of silver terminations or the giving off of vapors which would make soldering difficult or deteriorate the component properties or terminations by chemical action. In addition, the adhesive shall not become detached so that the components do not remain in position after storage and the carrier tape material shall therefore lose strength such that it breaks on unreeling when the taped components are fed from the package by hand or into the assembly machines. Removal of the top or bottom fixing tapes must not cause material to be removed from carrier tape and must not cause delamination of the carrier tape. The top tape shall be the fixing or cover tape on the outermost surface when the carrier tape is wound on a reel. Component identification marking, if used, shall face toward the top side of the tape. The bottom side of the chip, the side that contacts the printed circuit board, shall face the bottom tape. A maximum of 0.25% of the components per reel may be missing with no more than three consecutive components missing.
The prior art, as it has evolved, presents to the manufacturer and the use of leadless components several problems to which the present invention is directed. Among these problems are the cost of taping leadless or chip components, the cost of packaging the tapes of components and the delivery systems for feeding a plurality of reels to automatic placement equipment. In terms of cost, the manufacturers of chip components find that the cost of tape, reels and protective container for the reels of tape is currently 4 to 10 times the desirable goal.
Since the carrier tape is designed to hold chip components, it will have a certain thickness. In the prior art the thick portion of a carrier tape which, under the proposed standard, ranges from 0.94 millimeters and 1.75 millimeters in thickness, was traditionally made of a cardboard, chip board or similar substance which could be wound on reels. The carrier tape further included a cover tape on its bottom and a cover tape on its top, the function of the cover tape being to retain the components in position on the carrier tape. A major problem with the carrier tape of the prior art was that the tape has an inherent tendency to unwind from a reel and return to a linear position rather than a circular position, the clock spring effect. The reason for this tendency is obvious. When wound on a reel, the bottom of the tape has a tendency to be in compression whereas the top of the tape has a tendency to be in tension. Given the relatively rigid materials from which the tapes were made, the winding of the tape induced two effects, a clock spring effect whereby the tape has a tendency to unwind and to return to a normal linear position and a delamination of the top and bottom cover tapes which resist the compression and/or tension forces resulting from being wound on a reel.
A further problem arises with the user. The rolled tapes on reels tend to be difficult to handle. A stiff or relatively stiff tape when wound on a reel tends to have a clock spring action when the reel is removed from its package and the user begins to unwind the tape for feeding into a placement machine. This leads to unnecessary time delays and occasional mishandling of reels during loading, thus causing delays in the utilization of automatic placement equipment. Further, winding of a relatively thick carrier tape tightly around a reel having a relatively small hub causes delamination of the carrier tape and/or of the top and/or bottom cover tapes. In the process of winding, the bottom cover tape will tend to be in compression and tend to delaminate from the bottom of the carrier tape; whereas the top cover tape will have a tendency to be in tension, thereby tending to delaminate from the carrier tape. In the case of plastic embossed tape, there is no bottom tape and the compression is partially absorbed by the component cavities. Delamination of cover tapes is a serious problem because it causes chips to fall out of the cavities and thereby disrupt the automatic placement process. The goal of an automatic placement process is to limit failures to one or two parts per million. Delamination of the cover tapes can cause the failure rate to exceed acceptable tolerances.
It is essential to the understanding of a multi-chip packaging system that one recognize the fact that the major products of the system are disposable and/or non-reusable items. Specifically, the tape, the reel and, in the case of the prior art, the container, case or package in which the reel is stored and/or shipped prior to use are all throw-away items. Hence, it is essential that the cost of these items be reduced to a bare minimum in the design of any new and/or improved system. In the present invention, a major point of novelty is the fact that the engineered laminated structures which comprise the tape and the reel are basically paper structures with minimal use of thin plastic films and the reel and the tape when fully assembled form a selfsealing package.
The EIA standard covers two variations of tape for leadless components, a carrier tape and a plastic embossed tape. The present invention does not offer a variation of a plastic embossed tape for several reasons. In particular, the plastic embossed tape is costly and is subject to delamination of the cover tape when wound on reels. The plastic embossed tape also suffers from the clock spring effect, an effect which is virtually eliminated by the present invention.
For understanding this engineered laminated tape, the reader is referred to the EIA proposed standard referred to above. Insofar as possible, the terminology used in this specification will be consistant with that of this EIA standard.